Derivatives of 9,10-anthraquinone; emission spectra in polymer matrices at 77K and efficiency as initiators of degradation

Abstract

The emission spectra (phosphorescence) of 10 derivatives of 9,10-anthraquinone (2-methyl, 2,3-dimethyl, 2-ethyl, 2-isopropyl, 2- n-butyl, 2-tert butyl, 2-acetoxy, 2-octanoyloxy, 1-chloro and 2-chloro) in five polymeric matrices (polyethylene-PE, isotactic polypropylene-iPP, polystyrene-PS, poly(methyl methacrylate)-PMMA and poly(vinyl alcohol)-PVA were measured at 77K. In nonpolar hydrocarbon matrices vibrationally well resolved spectra were obtained which were dominated by the fundamental vibration of the carbonyl group (1680 cm −1). Lower vibrations in the region 700-250 cm −1 cannot be assigned unequivocally to active IR vibrations. In PS and PMMA matrices the fine vibration in the region 700-250 cm −1 is lost and the valence vibrations of the carbonyl group are shortened. In polar PVA the vibrational structure is completely lost and the intensity is decreased by a factor of 5–10. The life-time of monosubstituted derivatives of anthraquinone in PE, IPP, PS and PMMA lies in the range 2–4 ms. The 2,3-dimethyl derivative exhibits biexponential decay in PS and PMMA matrices. Since the emission of 9,10-anthraquinone derivatives in a PVA matrix was rather low, the life-time was not determined. The photo-degradation of PE, iPP and PS are accelerated by 9,10-anthraquinone and its derivatives and they themselves decompose in the first step of the degradation process. The 2- tert butyl derivative has been found to be the most effective photoinitiator for the polymers under study.